Acoustic measurements

The determination of sound power levels in the TRILUX laboratory takes place in a reverberation room according to EN ISO 3741 "Determination of sound power levels and sound energy levels of noise sources using sound pressure - Precision methods for reverberation test rooms" using elaborate decoupling measures from the ground as well as the environment. In this reverberant room with a volume of 200 m3 and ca. 200 tonnes of weight, sound sources generate a diffuse sound field. The basic sound pressure level in the reverberation room is ca. 4 dB(A), which results in a wide signal-to-noise ratio in relation to the measurement signal and thus creates the basis for reliable measurements.

Acoustic laboratory

To avoid standing sound waves, the reverberation room is constructed with oblique angles. The effect is that sound sources produce a diffuse sound field with proportionality between the measured sound pressure and the source’s sound power.

The reverberation room is calibrated using an officially examined standard sound source with established sound power levels in narrow frequency bands (mid-third/-octave frequencies).

In the reverberation room,

  • flow noise of ventilated luminaires in relation to extraction volume flow;

  • humming sounds of luminaires with magnetic/electronic control gear under operating conditions as well as

  • occurring clicking noises, e.g. in diffuser luminaires

are measured.

In the TRILUX laboratory for ventilation, climate and acoustic inspection, sound power levels and overall pressure losses in relation to air volume flow through ventilated luminaires are measured.

However, non-ventilated luminaires as well as their components can also generate noise, e.g. through vibrating lamination packs in magnetic control gear units or through the magnetic interaction of control gear units with their metal surroundings (control gear hum). Lamps and electronic control gear can also generate vibrations.

Quality products require highly diligent acoustic evaluation during luminaire development. This involves "artificial" degradation of luminaires before measurements, since their vibration characteristics strongly depend on use. Vibration resonance, caused e.g. by control gear, can occur even after longer periods of time due to fixings becoming loose or rigid, or due to changes in surface properties. Installation and contact surfaces between plastics and metals (e.g. between luminaire covers and luminaire housings) only gain their final friction properties, which are due to varying expansion coefficients of the adjacent materials and can give rise to the occurrence of clicking noises upon switching the luminaires on, after prolonged thermal strain.

Noise development in TRILUX luminaires is minimised using special construction measures to improve acoustic properties as well as corresponding measurements.

Figure b depicts the screen in the computer-aided measurement of a luminaire's acoustic data. The top field displays the frequency progression of the averaged sound pressure levels over a selected time span of 60 s as well as A-weighted (LPA) and linearly weighted sound pressure levels (LP). The centre field displays the instantaneous value and the lower field displays the temporal change in sound pressure during the measuring period of 60 s. The cursor in the bottom field can be used to display the frequency spectrum of an instantaneous value at a certain point in time in the centre field.

Long-term noise observation as well as targeted retrieval of individual sound pressure levels are possible, through which the causes for possible level peaks can be investigated. Those in turn impact luminaire construction.